rustc panics on compile-fail/borrowck/two-phase-reservation-sharing-interference

[cuviper]

This is another non-ICE panic revealed by #49891:

$ rustc +dev1 src/test/compile-fail/borrowck/two-phase-reservation-sharing-interference.rs -Z borrowck=mir -Z two-phase-borrows -Z two-phase-beyond-autoref
error[E0502]: cannot borrow `vec` as mutable because it is also borrowed as immutable
  --> src/test/compile-fail/borrowck/two-phase-reservation-sharing-interference.rs:46:9
   |
41 |         let shared = &vec;
   |                      ---- immutable borrow occurs here
...
46 |         delay = &mut vec;
   |         ^^^^^^^^^^^^^^^^ mutable borrow occurs here
...
50 |         shared[0];
   |         ------ borrow later used here

thread 'main' panicked at 'assertion failed: match borrow.kind {{
    BorrowKind::Shared => false,
    BorrowKind::Unique | BorrowKind::Mut {{ .. }} => true,
}}', librustc_mir/borrow_check/mod.rs:1252:13
note: Run with `RUST_BACKTRACE=1` for a backtrace.
error: aborting due to previous error

For more information about this error, try `rustc --explain E0502`.

[cuviper]

// The following revisions are disabled due to missing support from two-phase beyond autorefs
//[nll_beyond]compile-flags: -Z borrowck=mir -Z two-phase-borrows -Z two-phase-beyond-autoref
//[nll_beyond] should-fail

I'm not sure if should-fail is supposed to catch compiler panics, but I doubt it.

[sapphire-arches]

Anything involving two-phase-borrow-beyond-autoref is likely completely broken right now. We're not exactly sure if we're ever going to enable it (see #49434 for some context). That test variant should have been disabled, either you can go ahead and do it (by removing nll_beyond from this line) or I'll submit a PR doing exactly that.

[cuviper]

@bobtwinkles thanks, I added a commit to #49891 removing the bit you suggested.

[pnkfelix]

Re-triaging for #56754. Seems like PR #49891 addressed this. Closing as "fixed."